1. Field of the Invention
This invention relates to apparatus and method for facilitating the focusing of a camera having a displaceable lens whose position at which a subject is in focus is a predetermined function of subject distance.
2. Description of the Prior Art
Professional photographers usually utilize a camera with interchangeable, high quality lenses that allow the photographer the flexibility of choosing a lens suitable for the subject matter being photographed. Usually, an optical rangefinder is used by such photographers to adjust the position of the lens mount until the subject is properly focused. By accurately measuring the level of scene brightness and selecting a suitable diaphragm size and shutter speed, a sharply focused and properly exposed photograph will be obtained.
Not only does such an arrangement require manual ranging with its operator determination of range, but further it is very difficult and time consuming to use an optical rangefinder to accurately focus on the subject at low scene light levels because of the difficulty in clearly seeing the poorly illuminated subject. Consequently, photographs with less than desired image sharpness are sometimes obtained. Heretofore, short of adequately illuminating the subject to be photographed during focusing or utilizing a camera with an automatic focusing system based on ultrasonic ranging (such as disclosed in U.S. Pat. No. 4,199,244) very little could be done to facilitate proper focusing. Moreover, professional photographers usually prefer to have some manual control over these exposure parameters including focusing. Hence, the provision for rapidly obtaining sharply focused professional photographs, particularly under low ambient light conditions, has proved to be a difficult task.
It is therefore an object of the present invention to provide a new and improved apparatus and method for facilitating camera focusing. Another object is to provide an improved apparatus and method for facilitating manual or automatic focusing of photographic apparatus. A still further object is to provide a method and apparatus for automatically indicating the correct focal position while permitting the operator to maintain complete control over focusing.